This invention relates to obstetrics and in particular to probes for fetal monitoring.
The monitoring of the fetus is a vital aspect of modern labour management. Assessment of the fetal heart rate is a mainstay of such monitoring and can be done externally or by internal electrodes. In certain circumstances, internal monitoring is preferred and provides a more accurate representation of the fetal heart rate pattern for analysis. Internal monitoring probes are usually made of arcuate or spiral metal needles which perforate the scalp skin and are thus secured to obtain electrical signals from the fetal heart. Such probes can be considered invasive to the fetus.
Alternatively, intrauterine probes have been designed which do not have to perforate the fetal skin and which have contact electrodes that lie opposed to the surface of the fetal body and scalp. Reference is directed for example to U.S. Pat. No. 3,326,207 and GB-A-2,195,877. These probes are long and have several built-in electrodes to ensure that at least one of them is in sufficient contact with the fetal skin to obtain an adequate signal. Another sensor, some distance away, is used as a reference electrode. Unless already ruptured spontaneously, the membranes of the amniotic sac have to be ruptured artificially before such a probe is inserted. Because of this aspect and its overall length, such probes can be considered invasive to the mother and the uterine environment of the fetus.
The probe disclosed in GB-A-2,195,877 comprises an elongate flexible strip having a series of protruding electrodes. The strip is of sufficient length (approximately 50 cm) to extend past the fetal head and along the trunk of the fetus. U.S. Pat. No. 3.328,207, issued in 1967, proposed a fetal probe having two inflatable balloons positioned as to contact the shoulder and hip/thigh regions of the fetus, respectively. Each balloon is spherical and carries six or so equatorially spaced electrodes. Additionally, each electrode is provided with a port for the local discharge of a conductive solution. The construction and operation of this probe is considered to be far too elaborate and cumbersome for practical application.
It is an object of this invention to provide an improved a fetal probe which is not invasive to the mother or the fetus.
Accordingly, the present invention consists in one aspect in a fetal probe comprising an elongate body portion adapted for insertion into the cervix around the presenting pact of the fetus, the body portion carrying fetal sensor means; characterised in that the body portion is insertable into the cervix to a length of between 10 and 20 cm and preferably about 15 cms enabling positioning of the probe such that the sensor is held against the fetal presenting part by the pressure of maternal tissue with the amniotic membrane intact.
The probe according to this invention can be inserted through the vagina into a cervical opening of 1 cm or more dilatation, with the most distal part of the probe extending into the lower part of the uterus only, inside the cervix and just above the presenting part. The amniotic membranes do not necessarily have to be ruptured to enable this insertion.
The probe can be a vehicle for a variety of monitoring functions, and the probe sensor means can take a variety of forms. Principally, the sensor means would comprise a contact electrode for obtaining the fetal heart rate signal, a using a record, reference electrode positioned on the maternal surface of the near end of the probe, to be in contact with vaginal tissues. In addition, the probe can contain the sensors (photodiode and light emitting diodes (LED""s)) for transcutaneous pulse oximetry. Other sensors can else be built in to measure other parameters. It has been found that most sensors can detect a satisfactory signal through intact amniotic membranes.
According to this invention, the probe can be held in place by the pressure of maternal tissues (cervix, vaginal) against the fetal presenting part but additionally it can also be secured non-invasively by an inflatable semi-cuff or balloon at the distal end of the probe. This balloon can be made of a thin plastic or synthetic-rubber material and is confined to the maternal surface of the probe. Therefore inflation will result in the fetal surface of the probe being approved to the fetal skin, thus insuring good contact for the built-in sensors which are located nearby. The inflated balloon also a the probe from slipping out of the cervix and vagina during maternal movement, contractions and fetal descent, until such time that the fetal presenting part is delivered or the balloon is deflated for probe removal. As the balloon a above the presenting part, it does not interfere with its descent during labour.
Another advantage of the balloon at the distal end of the probe is that after probe insertion and balloon inflation, gentle traction on the probe will reliably find a point of optimal contact between the main sensor area of the probe and the skin of the presenting part.
According to another feature of this invention, there are one or more channels running the whole length of the probe which can be used for access into the uterus around the presenting part, without the need for an additional vaginal examination.
One beneficial use for such an access channel is for rupturing the amniotic membranes by inserting a special canula to apply localised suction or contact-glue before rupturing the membranes by traction; alternatively a small hooked or sharp-tipped flexible trocher can be inserted to perforate the membranes. Rupturing the membranes in this area above the presenting part, i.e. the xe2x80x98breaking the hindwatersxe2x80x99, is already done occasionally by a special canula (Drews-Smyth canula) and can have the following advantages over forewater membrane rupture:
1. In cases of poor engagement of the presenting part, hindwater rupture reduces the possibility of prolapse of the umbilical cord. This is the main indication for using a Drews-Smyth canula in clinical practice today, but these canulas are now rarely used because their rigid, curved shape have occasionally caused injury; it a suggested that the pliable, flexible probe of the present invention would make this procedure more safe.
2. In cases of good engagement of the presenting part, the membranes may be tightly applied to the skin (usually scalp) of the baby and a conventional amniotomy hook may scratch the skin surface as the membranes are being ruptured. Sometimes, no amniotic fluid is obtained and there is uncertainty as to whether the membranes are still intact. These problems are avoided by rupture of the membranes above the presenting part where there is more amniotic fluid.
The access channel can then be left open to allow amniotic fluid to escape even when the presenting part would otherwise, due to a tight fit, be sealing the pelvic outlet; thus the presence of meconium would still be noted on inspection.
Another possible use for such an access channel is the insertion of an intrauterine pressure catheter or transducer. When, during labour, it becomes apparent that such a catheter needs to be inserted for pressure monitoring, an often distressing additional vaginal examination for this insertion can be avoided and the already in-situ probe of the present invention can be used to guide the tip of the catheter through it and around the presenting part up into the uterus. The additional cost of using a long pressure catheter is reserved for those cases where it becomes actually necessary as labour progresses, while the discomfort of an extra, intracervical digital examination is avoided. By taping the proximal ends of the pressure catheter and the probe of the present invention together, the balloon which is securing the probe in place also ensures that the pressure catheter does not slip out due to maternal movement or accidental pulling by an attendant.